The long-term goal of this research is to explore the molecular mechanisms that bacteria use for intra-and inter-species cell-cell communication. The objective of this proposal is to identify and study the model Vibrio harveyi signal transduction pathway that links detection of extracellular quorum sensing signal molecules termed Al-I and Al-2 to target gene responses. Definition of the genes, proteins, protein-protein interactions, protein modifications and signaling molecules involved in this cell-cell communication system will lead to a molecular understanding of how signals are detected and how this information is integrated, processed, and transduced to control behavior on a community scale. Analyzing the V. harveyi quorum sensing signaling circuit should be valuable for understanding how bacteria perceive and react to their environment, how they respond to temporally coincident cues, and how they communicate with one another to coordinate behavior. Since the regulatory process is complex and involves both intra-species, inter-species, intra-cellular and inter-cellular signal transmission, interesting new mechanisms should be revealed